The road's circadian signal

The Quinto case made it plain: sleepiness at the wheel can be difficult to recognise beforehand and establish after a crash. Inside the car a signal is arriving, onboard warning systems are becoming mandatory in Europe; on the road, a signal that warns beforehand - when sleepiness tends to weigh most - does not yet exist. We built this tool as the first prototype of that signal: not a sensor that catches you already sleepy, but a reminder that comes before.

The tool uses no traffic data and no personal data. The curve reflects the circadian rhythm of alertness documented by chronobiology: the drive to sleep peaks at night, roughly between 2 and 6, with a second dip in the afternoon. In sleep-related crashes, Horne and Reyner found three peaks: around 2 am, 6 am and 4 pm. It is a population model, not a measurement of the individual: it helps recognise the windows, not certify a state. The science that aims to measure sleepiness for real, in the clinic and in the body's biochemistry, is told in How sleepiness is measured.

Set your departure time and the length of the trip. The curve shows how sleepiness runs across the 24 hours; the highlighted band is your journey, and the tool tells you if and around what time you cross the critical window. You can drag on the curve or use the sliders; Now returns to the real time. If the trip touches a critical window, the simplest thing is to shift your departure or plan a short break before setting off.

It is an educational indicator, not a diagnosis. The real rhythm varies from person to person - chronotype, sleep debt, shift work, health - and must be verified in real driving. No alertness window authorises driving while sleepy: if you are sleepy, you do not drive. The tool helps you plan, not justify.